ABSTRACT
The field of microencapsulation and nanoencapsulation is concerned with a large number of processes used to produce particles of defined size and structure. Encapsulation processes are generally classified under chemical, physicochemical, and mechanical processes, including many subcategories such as polymerization, polycondensation, spray drying, coacervation, solvent evaporation, etc. However, these terms do not completely describe the principle of particle formation and the mechanisms involved. These mechanisms include phase separation, precipitation, interfacial polymerization or polycondensation, crosslinking, and gelation. All these refer to the generation of particles from an initial phase, which can be a solution or more frequently a dispersion (emulsion or suspension). This initial stage is a fundamental step in the encapsulation process, especially when an emulsion or a suspension is concerned, as it directly influences the final properties and, most importantly, the size of the particles. Other classifications could be based on the mechanisms involved, on the nature of the continuous phase, or on the starting materials. A distinction is commonly made between the processes using polymer as encapsulating material and the others that involve monomers and are based on a chemical reaction (so called chemical processes). It can also be considered that a great difference exists between processes occurring in liquid phases or in gas phases. The former are the majority of chemical and physicochemical processes, generally based on the formation of an initial dispersion in an aqueous phase followed by a transformation of the droplets or fine particles in capsules or spheres. The latter belong to the mechanical processes category, based on the dispersion of the initial phase (solution or dispersion) in a gas stream. Whatever the classification adopted, an encapsulation process can be defined by the different basic steps of the particles formation, the mechanisms involved at each stage, and the technical means employed. The simultaneous consideration of
technical aspects and mechanisms occurring is necessary because of the influence of the production techniques and conditions and the mechanisms (1).
